For those who like to grow plants, flowers, and vegetables from heirloom seed varieties that are not genetically modified or hybridized to the point where you lose the character and flavor of the vegetables to American commercial homogenization, you have several affordable options:
The two companies that I have personally ordered from and had good experiences with are:
Seed Savers Exchange based in Iowa. Their live tomato seedling transplants are really good. I highly recommend the Cherokee Purple tomatoes.
Baker Creek Seeds is another good one. They have an incredible selection that I have never seen before.
I have recently heard of a few seed co-ops that also do good work but I have never ordered from personally:
SeedsNOW! which has a handy Online Gardener's handbook that is free to access.
High Mowing Organic Seeds (free shipping) that I just heard about on one of the Facebook groups that I joined that are dedicated to Heirloom seeds and people were raving. Worth a try as well.